According to URA, prices, as well as the number of units sold during the month, are based on the Option-to-Purchase issued by developers to buyers. An Option-to-Purchase is a right or option given by the vendor to an intending purchaser to buy the property at a specified price within a specified period of time - the validity period of the option. The intending purchaser must pay a booking fee of between 5 – 10 percent of the agreed price for this right or option. The purchaser has to exercise the Option-to-Purchase within its validity period if he decides to buy the property.